We will continue to explore the relationships between the intake of individual essential amino acids, their plasma concentrations and the requirement for them. We consider it highly desirable to incorporate into our studies a more detailed evaluation of N balance, despite its shortcomings, along with an assessment of the plasma amino acid levels in relation to level of intake. We will continue to examine the plasma valine response in elderly subjects, and begin to examine the isoleucine, lysine and phenylalanine response curves. Emphasis will also be placed on a test range of intake from a level which is supplied by the safe practical allowance of egg protein to level below those reported by Rose et al. and Leverton et al. as being adequate for N balance in adult subjects. This will allow us to more critically assess the significance of plasma amino acid concentrations and their relevance to nutritional requirements.